JP2517645B2 - Optical recording medium - Google Patents

Description

The present invention relates to an optical recording medium, and more particularly to a card-shaped optical recording medium for optically recording / reproducing information.

[Conventional technology]

In recent years, with the progress of informationization in society, as a means for efficiently handling a wide variety of information, there are many information record carriers and information recording / reproducing devices that record or reproduce optical information such as optical discs, optical cards, and optical tapes. Proposed. Some of the information record carriers can detect binarized information by converting it into a change in the reflectance and a change in the intensity of reflected light associated with a change in the surface shape such as the presence or absence of a pit (hole).

A so-called heat mode recording material has been proposed as a record carrier based on a change in optical reflectance, in which a recording layer is irradiated with an energy beam such as a laser beam in a spot shape to change a part of the recording layer for recording. ing. These recording materials require so-called DRAW [direct read after write (direct read af
ter write)] medium and high density recording is possible,
Additional writing is also possible.

In the optical information recording / reproducing device,
There is a system in which grooves are formed in advance on the medium surface at regular intervals for read-out track servo. In this method, the groove plays a guiding role for reading, so that the track control accuracy of the laser beam is improved, and higher-speed access is possible as compared with the conventional method using the grooveless substrate.

When the track groove is formed on the substrate, when the substrate is a thermoplastic resin, the stamper mold is thermally transferred by a method such as injection molding or hot press molding at a temperature equal to or higher than the melting point, or a light is transferred onto the substrate. A method of optically transferring a stamper mold by a method of applying a curable resin composition, bringing the stamper mold into close contact, and irradiating with ultraviolet rays or the like to cure the photocurable resin composition has been conventionally known.

Next, a conventional card-shaped optical recording medium (hereinafter referred to as an optical card) will be described as an example of the optical recording medium.

A transparent substrate having a track groove 26 in FIG. 2 (a)
An optical recording layer 22 is formed by coating on 21 and an opaque card base material 24 is bonded via an adhesive layer 23 for the purpose of protecting the optical recording layer.

As shown in FIG. 2 (b), the first few to several tens of the tracks provided on the optical card surface are formed with a start point indicating the start of the recording / reproducing area. The area 30 and, similarly, the last few tracks to several tens of tracks are the stop-pit forming areas 31 indicating the end of the recording / reproducing area. These start pits and stop pits are called pre-format signal pits and are formed in advance on the transparent base material like the track grooves.

By the way, in the conventional optical card, the pre-format signal pits are formed on several tracks to several tens of tracks just inside the outermost track groove, but when the optical recording layer is formed by coating on this recording / reproducing area, The film thickness becomes thin on the track around the recording / reproducing area, that is, on the track at the end of the recording / reproducing area where the pre-format signal pits are formed, and the reflectance of this part decreases or becomes non-uniform. There are problems that the C / N value of the reproduction signal of the pre-format signal pit formed on the track at the end of the area is lowered, and that a reproduction error occurs and the reproducing device does not operate.

The reason why the film thickness at the peripheral portion becomes thin is that when the optical recording layer material is dissolved or dispersed in a solvent and applied, it is dried from the surroundings and the optical recording layer material is formed at the boundary between the dried portion and the undried portion. It is thought that this is due to the movement to the undried portion.

[Problems that the invention is trying to solve]

An object of the present invention is to provide a highly reliable optical recording medium by making the film thickness of the optical recording layer in the track portion of the recording / reproducing area uniform.

[Means for solving problems]

The optical recording medium of the present invention is an optical recording medium having a substrate on which a concavo-convex pre-format is formed and a recording layer formed by coating, and the substrate is provided outside the track on which the pre-format signal pit is formed in parallel with any track groove. It is characterized by having at least one groove having a cross-sectional shape.

That is, since the peripheral portion of the thin optical recording layer remains in the dummy groove formation region, the film thickness of the track portion where the pre-format signal pit is formed at the end of the recording / reproducing region,
The difference from the thickness of the central portion of the recording / reproducing area is reduced.
Therefore, the reflectance of the track portion where the pre-format signal pit is formed is reduced and the unevenness of the reflectance is reduced, and the reading error of the signal pit formed on the track at the end of the recording / reproducing area can be prevented. .

 Next, the present invention will be described in detail with reference to the drawings.

1 (a) and 1 (b) are a sectional view and a plan view showing an embodiment of the optical recording medium in the present invention.

That is, at least one groove having an arbitrary cross-sectional shape is formed in parallel with the outermost track groove in which the pre-format signal pit is formed (hereinafter, this groove is referred to as a dummy groove). The width, depth, and pitch of the dummy groove 27 are selected depending on the width, depth, and pitch of the track groove in the recording / reproducing area, but the width is 0.6 μm to 6 μm, the depth is 0.05 μm to 0.5 μm, and the pitch is 1.2 μm to 15 μm. Within the range of 1 μm to 5 μm
m, depth 0.1 μm to 0.5 μm, pitch 9 μm to 12 μm are preferable. Further, the width and depth of the groove may be changed stepwise. Although the cross-sectional shape of the dummy groove is arbitrarily selected, the same shape as the cross-sectional shape of the track groove is preferable.

Further, as a method of forming the dummy groove, it is preferable that the dummy groove is formed at the same time as the formation of the track groove and the pre-format signal, in that it is formed in parallel with the track groove on the substrate.
It may be provided before or after the track groove and the pre-format signal pit are formed on the substrate. The range of the dummy groove formation region is not particularly limited as long as it is above the start pit formation region and below the stop pit formation region. 1 mm to 5 mm on the upper side and on the lower side of the stop pit forming area is preferable.

Further, it is desirable that the dummy grooves are provided on both sides of the upper side of the start pit forming area and the lower side of the stop pit forming area, but they may be provided on only one side.

The present invention is also effective in the case of an optical disk, in which case the dummy groove is provided in the inner peripheral portion and / or outer peripheral portion of the recording / reproducing area. At this time, the dummy groove forming area is preferably 1 mm to 5 mm inside and / or outside the recording / reproducing area.

As the transparent substrate 21 having the track groove 26, the pre-format signal pit, and the dummy groove, those having little inconvenience in optical recording / reproducing are preferable, and for forming the track groove, the pre-format signal pit and the dummy groove. A thermoplastic material having good moldability is preferable. For example, acrylic resin, polyester resin, polycarbonate resin, vinyl resin, polyimide resin, polyacetal resin, polyolefin resin, polyamide resin, cellulose derivative and the like can be used.

As the opaque base material 24, any material that can be used as a normal base material can be used, and specifically, polyvinyl chloride, vinyl chloride / vinyl acetate copolymer, polyvinylidene chloride, polymethyl methacrylate, etc. Acrylic polymers, polystyrene, polyvinyl butyral, acetyl cellulose, styrene / butadiene copolymers, polyethylene, polypropylene, polycarbonate and the like are used. Depending on the case, a metal sheet of iron, stainless steel, aluminum, tin, copper, zinc or the like, synthetic paper, paper or the like can be used. Furthermore, a laminate of the above materials can also be used. If necessary, these opaque base materials 24 may be subjected to a pretreatment such as corona discharge treatment, plasma treatment, or primer treatment for improving the adhesiveness.

As the optical recording layer 22, the wavelength of the reproduction energy beam is
When the thickness is 650 nm or more, particularly 700 to 900 nm, it is preferable that the difference between the reflectance in the pit which is the recorded portion and that in the unrecorded portion is large. Further, it is preferable that the energy required for changing the reflectance due to the irradiation of the energy beam for recording is small. Further, it is preferable that the reflectance of the recorded portion and the unrecorded portion does not change due to the reproducing energy beam. For example, oxides such as Te, Sb, Mo, Ge, V, and Sn, compounds such as Te-Sn, and TeO _x -Ge undergo phase transition upon irradiation with an energy beam, and the reflectance changes. _{Furthermore, Te-CH 4, Te-} CS 2, Te- _{styrene, Sn-SO 2, GeS-} Sn, S
A composite of a metal such as nS-S and an organic compound or an inorganic sulfide, or a multilayer film such as SiO ₂ / Ti / SiO ₂ / Al can also be used.

Further, it is also possible to use a material in which metal particles such as silver are dispersed in a thermoplastic resin such as nitrocellulose, polystyrene or polyethylene, or a material in which metal particles are agglomerated on the surface of this thermoplastic resin. The chalcogen or coloring type of MoO ₃ -Cu, also used such as MoO ₃ -Sn-Cu,
Depending on the case, a multilayer body of a foam-forming organic thin film and a metal thin film can also be used.

Further, an organic thin film whose optical properties can be changed by an energy beam can also be used, for example, an anthraquinone derivative,
In particular, those having an indasulen skeleton, dioxazine compounds and derivatives thereof, triphenodithiazine compounds, phenanthrene derivatives, cyanine compounds, merocyanine compounds, pyrylium compounds, xanthene compounds, triphenylmethane compounds, croconium dyes, crocones, etc. The above dyes are preferable, and they are preferable for the present invention because they can be continuously produced by solution coating.

〔Example〕

Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited thereto.

Example 1. As a transparent substrate, a track groove, a preformat signal pit and a dummy groove were formed on a polymethylmethacrylate film (manufactured by Nitto Plastic Co., Ltd.) containing a 0.4 mm thick ultraviolet absorbent by a hot pressing method. Track groove pitch 10μ
m, track groove width 3 μm, groove depth 0.2 μm, and dummy groove has pitch 10 μm and dummy groove width 3 μ like the track groove.
m, the depth of the dummy groove was 0.2 μm, the distance between the track groove and the dummy groove was 7 μm, and the dummy groove forming region was 4 mm above and below the start pit forming region and the stop pit forming region. Then, 1,1,5,5-tetrakis (p-diethylaminophenyl) -2,4-pentadienium perchlorate was added to diacetone on the recording / reproducing area where the track groove was formed and the area where the dummy groove was formed. The solution dissolved and dispersed in alcohol was applied by spin coating so that the dry film thickness of the track portion at the center of the recording / reproducing area was 1000Å, and dried.

A 0.3 mm thick polycarbonate plate was adhered as an opaque substrate through an ethylene-vinyl acetate copolymer adhesive (trade name Hirodyne 7500 EXP-80; manufactured by Hirodyne) to manufacture the optical recording medium of the present invention. .

This optical recording medium is irradiated with a semiconductor laser beam with an oscillation wavelength of 830 nm and a power of 0.4 mW from the transparent substrate side, and the reflectance (R ₁ ) of the outermost track on which the pre-format signal pit is formed and the center of the recording / reproducing area The reflectance (R ₂ ) of some tracks was measured.

Then, the pre-format signal pit formed on the outermost track of the recording / reproducing area was reproduced with a semiconductor laser beam having the same wavelength and the same power, and the probability of tracking deviation (tracking error rate) was measured.

Comparative Example 1. An optical recording medium was manufactured in the same manner as in Example 1 except that the dummy groove formed in Example 1 was omitted. The reflectance (R ₁ ) of the track on which the pre-format signal pits of this optical recording medium are formed and the reflectance (R ₂ ) of the track at the center of the recording / reproducing area were measured.

Then, the pre-format signal pit formed on the outermost track of the recording / reproducing area was reproduced with a semiconductor laser beam having the same wavelength and the same power, and the tracking error rate was measured. The results are shown below.

EFFECTS OF THE INVENTION As described above, according to the present invention, the difference between the film thickness of the recording layer on the track at the end of the recording / reproducing area and the film thickness of the recording layer on the track at the center of the recording / reproducing area is determined. It can be made smaller, the reflectance of the track part of the recording / reproducing area due to the reproduction light can be made uniform, the probability of the track part being out of the track part at the end of the recording / reproducing area can be reduced, and reading errors can be prevented. can do.

[Brief description of drawings]

FIG. 1 (a) is a schematic sectional view of one embodiment of an optical recording medium according to the present invention, FIG. 1 (b) is a plan view thereof, and FIG. 2 (a) is a conventional optical recording. FIG. 2 is a schematic sectional view of the medium, and FIG. 2 (b) is a plan view thereof. 21 ... Transparent substrate, 22 ... Optical recording layer 23 ... Adhesive layer, 24 ... Opaque card base material 26 ... Track groove, 27 ... Dummy groove 28 ... Recording / reproducing area 29 ... Track forming area 30 ... … Start pit formation area 31 …… Stop pit formation area 32 …… Dummy groove formation area

Claims (1)

(57) [Claims] 1. An optical recording medium having a substrate on which a concavo-convex pre-format is formed and a recording layer formed by coating, wherein the substrate has at least one groove outside the track on which the pre-format signal pit is formed and in parallel with the track groove.
An optical recording medium having at least two.